1. Field of the Invention
The present invention relates to a print method and a print apparatus for printing an image on the obverse surface of a print medium, then reversing, inverting and conveying the print medium and forming an image on the reverse surface of the print medium.
2. Description of the Related Art
Currently, a print apparatus, such as a printer, is known that has an automatic double-sided printing function whereby an image can be automatically formed on both the obverse surface and the reverse surface of a print medium. In the print apparatus, first, a print medium supplied by a supply unit is conveyed to a location opposite a print head. Then, the print head performs the printing of the print medium that has reached to the location opposite the print head. Thereafter, the print medium is inverted and reversed, and is again conveyed to the location opposite the print head. Following this, the reverse surface of the print medium, which has been conveyed to and positioned opposite the print head, is printed to obtain a double-sided print medium image.
An example print apparatus having an automatic double-sided printing function is disclosed in Japanese Patent Application Laid-open No. 6-183068. FIG. 11 is a diagram showing the thus disclosed print apparatus. During a single-sided printing process performed by a print apparatus 300, a switching guide member 260 is held at a location indicated by solid lines. Therefore, after a print medium 1, supplied from a paper supply stacker 210, has been printed by a print head 250, the print medium 1 is passed on to the switching guide member 260 and is discharged to a discharge stacker 280, as indicated by an arrow b.
During a double-sided printing process performed for print media P, the position of the switching guide member 260 is changed to a location indicated by broken lines. Therefore, after the print medium 1 has been supplied from the paper supply stacker 210 to the print head 250 and one side has been printed, the print medium 1 is conveyed to a reverse unit 350, as indicated by arrows F and G. Thereafter, the print medium 1 is transported from the reverse unit 350 toward a reverse roller 340 in a direction indicated by an arrow H, which is opposite the direction indicated by the arrow G. Then, the print medium 1 is conveyed by the reverse roller 340, a guide plate 360 and a transport roller 310. Upon reaching the transport roller 310, the print medium is fed along a guide 320 by the impelling force exerted by the transport roller 310. Thereafter, the print medium 1, which has been inverted and reversed, is again guided to the print position opposite the print head 250 and the reverse surface is printed. After the printing of the reverse surface has been completed, the switching guide member 260, displaced by being rotated downward, guides and discharges the print medium 1 to the discharge stacker 280.
The print apparatus 300 disclosed in this publication encloses an image by providing margins at the edges of a print medium P and by controlling the widths of right and left print margins.
Owing to recent improvements in printing technology, print apparatuses are now available for which high-quality image forming, equivalent to that of silver halide photography, is available. Among the print apparatuses for which high-quality image forming is enabled, proposed are print apparatuses capable of performing so-called marginless printing (hereinafter also called full printing) whereby, as in silver halide photography, the provision of margins at the edges of a print medium is not required, and an image can be formed across the entire surface.
A print apparatus that performs the above described full printing is disclosed in Japanese Patent Application Laid-open No. 2003-177898 (US-2003-0053096). This print apparatus not only performs printing in an area inside the edges of a print medium, but also ejects extra ink (coloring material) within a range projecting outward several millimeters from the edges of the print medium. With this arrangement, the formation of margins at the edges of the print medium is prevented, and full printing is ensured. Furthermore, during the marginless printing process, ink ejected outside the edges of the print medium lands on, and is absorbed by, an ink absorption member provided for a platen.
Both the print apparatuses described as conventional examples, the one that performs double-sided printing and the one that performs full printing, are well known. However, when a print apparatus having a double-sided printing function, as disclosed in Japanese Patent Application Laid-open No. 6-183068, performs a full printing operation, as disclosed in Japanese Patent Application Laid-open No. 2003-177989 (U.S.-200300053096), the following enumerated problems have been encountered, and under current conditions, print apparatuses having automatic double-sided printing mechanisms that can perform full printing are not yet commercially available.
Specifically, since print media used for a print apparatus are prepared by cutting a paper roll to obtain a predetermined size, slight cutting errors can occur at either the leading edge or the trailing edge and at either the right or left edge of each print medium. Assume that the width (hereinafter referred to as an overrun distance) of a designated area (hereinafter referred to as an overrun area), extending outward from and enclosing a print medium, into which extra ink is to be ejected is based on an ideal print medium for which there are no cutting errors. The probability then exists that a portion wherein no printing is performed, i.e., a margin, will be formed at either the leading edge or the trailing edge, and either at the right edge or the left edge of the print medium.
Therefore, for a conventional print apparatus that performs full printing only on one side of the print medium, a setup for the overrun distances from the edges is performed as shown in FIG. 12A. As for the four edges P1 to P4 of a print medium P, the overrun distances from the edges P2 (second edge) and P4 (fourth edge), whereat, respectively, there are cutting errors B and D, are set so as to be greater than the overrunning distances from the edges P1 (first edge) and P3 (third edge), whereat there are no cutting errors B and D. That is, an overrun distance A is set for the first edge P1, while taking into account the positioning error (the search accuracy) between the location of the leading edge of the print medium in the conveying direction and the print position of the print head. On the other hand, an overrun distance (A+B), obtained by adding the cutting error B to the overrun distance A, is set for the second edge P2.
Furthermore, an overrun distance C is set for the third edge P3, while taking into account an error that occurs due to the obliquely parallel movement of the print medium P. Whereas, an overrun distance (C+D), obtained by adding the cutting error D to the overrun distance C, is set for the fourth end P4. When the overrun distances are designated in this manner for the individual edges of the print medium P, an appropriate image can be printed for which there are no margins at the edges of the print medium.
According to a print apparatus having the automatic double-sided printing mechanism described in Japanese Patent Application Laid-open No. 6-183068, during the double-sided printing process, the obverse surface and the reverse surface of the print medium are reversed, and the leading edge and the trailing edge of the print medium are inverted. That is, in the printing process for the obverse surface, the second edge P2 is located at the rear in the conveying direction (the X direction), while in the printing process for the reverse surface, the second edge P2 is positioned at the front in the conveying direction (the X direction), as shown in FIG. 12B. Then, the overrun distance from the edge P1 of the print medium, is A for the obverse surface printing, and A+B for the reverse surface printing. Further, the overrun distance, from the edge P2 of the print medium, is A+B for the obverse surface printing, and A for the reverse surface printing. Therefore, as indicated by α in FIG. 12, the position of the entire image data relative to the print medium differs as to the obverse surface and the reverse surface.
Therefore, when, for example, an extended image is to be formed across the reverse surface of a print medium and the obverse surface of the following print medium, the continuity of the right segment of the image and the left segment of the image is lost. As a result, the quality of the extended image is deteriorated.